The suspected mastermind of the plot to kidnap reporter Daniel Pearl is the target of an active grand-jury investigation in the United States, which is also looking into other kidnapping plots involving U.S. citizens dating back to 1994.

Justice Department sources told Newsweek magazine that British-born Islamic militant Ahmed Omar Saeed Sheikh – also known as Sheikh Omar – could be indicted in a matter of weeks, and the United States would then seek his extradition.

As Pakistani police continued to interrogate Omar, cops were combing the Punjab province.

They said they were hot on the heels of the man known as Imtiaz Siddiqui, who they now believe carried out the kidnapping in Karachi three weeks ago and may still be holding Pearl.

With the fate of the Wall Street Journal reporter still uncertain, FBI officials in Washington were said to be furious that Pakistani officials kept Omar’s arrest secret for a full week.

Omar surrendered on Feb. 5, but Pakistan’s powerful Inter-Service Intelligence Agency (ISI) held him incommunicado until Feb. 12 before turning him over to police.

According to Pakistani police, Omar and his accomplices belong to Jaish-e-Mohammed, a militant Islamic group with ties to al Qaeda that has long been involved in the struggle for control of the disputed Himalayan border region of Kashmir.

Until they were banned by President Pervez Musharraf, such groups had the covert support of the ISI and Omar himself was probably an ISI “asset,” a senior Pakistani official told Newsweek.

The source suggested that the ISI, aware that the kidnapping was deeply embarrassing to Musharraf, tried and failed to make a deal for Pearl’s release.

The Washington Post reported yesterday that Omar told his interrogators the kidnapping was a “warning shot” to the Pakistani president for his crackdown on militant Islamic groups.

He said that three recent attacks in India were also intended to undercut Musharraf’s efforts to curb the activities of extremist groups in response to pressure from the United States.

In a Karachi courtroom last week, Omar admitted kidnapping Pearl and said he believed the reporter was dead. But Pakistani officials said he was bluffing.